1. Field of the Invention
The present invention relates generally to interactive television systems. More specifically, the present invention relates to a method and system for synchronizing multiple signals received through different transmission mediums, such as, for example, a cable television signal and a radio signal transmitted via the Internet.
2. Description of Related Background Art
In recent years, the number and quality of transmission mediums for disseminating information and entertainment have greatly expanded. For example, only a few years ago, transmission options were limited to television and radio broadcasts via electromagnetic waves (e.g., VHF, UHF, AM, FM). Today, audio, video, and data transmissions may be received through cable and satellite systems, broadband radio-frequency systems, digital telephone networks (e.g., DSL, ISDN), packet switched networks (e.g., the Internet), and the like.
In many cases, it is advantageous to combine signals received through different transmission mediums. For example, it may be advantageous to combine a cable television signal with a streaming video signal received via the Internet. Likewise, it may be desirable to combine a data transmission received via the Internet with a satellite television signal (e.g., DSS).
Each transmission medium has a particular bandwidth, i.e. the amount of data that can be transmitted in a fixed amount of time. One transmission medium, such as a cable network, might have a relatively high bandwidth, e.g. 10 megabits per second (Mbps), while another medium, such as a DSL or analog telephone line, might have a lower bandwidth, e.g., 256 or 56 kilobits per second (Kbps), respectively. Thus, certain transmission mediums might be better suited to video distribution (which requires a higher bandwidth) while other transmission mediums might be better suited to audio or data distribution (which typically requires a lower bandwidth).
Each transmission medium is also associated with a particular latency, i.e. the time it takes for information to travel from a source computer to a destination computer. For some transmission mediums, such as a cable network, the latency is relatively low. However, in the context of a packet switched network, such as the Internet, the latency can be as high as several seconds.
Differences in latency between two transmission mediums (and other factors) can cause two signals transmitted simultaneously via the different mediums to arrive at different times. Where the delay in receiving the second signal is greater than a few seconds, directly combining the two signals may be undesirable due to the lack of synchronization.
As an example, both radio and television stations traditionally provide coverage for sporting events, such as football, basketball, baseball, etc. Indeed, multiple radio and television stations typically cover an event for both local and national audiences.
Although television offers the apparent advantage of allowing a person to see the sporting event, many prefer the radio for a number of reasons. For example, radio announcers often provide a better commentary since they must rely on words alone to describe the event. Moreover, radio broadcasts typically include fewer commercials, interviews, human interest stories, or the like, which tend to interrupt the event.
To obtain the advantages of both radio and television, some people watch a televised sporting event with the volume muted, while simultaneously listening to a radio commentary by their favorite announcer. As a result, the viewer obtains the benefits of better commentary, fewer interruptions, and the like, while also being able to watch the event. This approach is possible because electromagnetic broadcasts of television and radio signals are typically received at same time with little or no relative delay (both transmissions travel at the speed of light).
Unfortunately, listening to radio coverage of a televised sporting event may not always be possible. For example, for events in remote cities, there may be no locally-broadcast radio coverage. In addition, a user may not be aware of which events are being broadcast on which radio stations.
Today, radio programs are beginning to be broadcast via the Internet. Radio signals are digitized, packetized, and transmitted to a receiver""s computer using standard protocols such as TCP/IP (transmission control protocol/Internet protocol). Various standard software programs are available for receiving and playing radio signals transmitted via the Internet, such as RealPlayer Plus(copyright), available from RealNetworks, Inc. of Seattle, Wash.
Advantageously, Internet-based radio transmissions are not geographically limited. Thus, a local radio station in New York City may be received via the Internet at a user""s home in Seattle or anywhere else in the world. It is now possible to choose from radio broadcasts from thousands of radio stations around the world via the Internet medium.
Unfortunately, the process including digitizing the radio signal, establishing a communication channel, and transmitting the radio signal via the Internet introduces a delay of several seconds when compared to a television signal transmitted, for example, via a cable network. Moreover, an Internet radio signal may be delayed with respect to a television broadcast for contractual reasons. Thus, the Internet-based radio coverage of a sporting event is delayed in time with respect to the television coverage, making a direct combination of the two undesirable due to lack of synchronization between the two signals.
What is needed, then, is a system and method for synchronizing and combining multiple signals received through different transmission mediums, such as a television signal received through a cable network and a radio signal sent via the Internet.